Use hardware timer to simulate interrupt moderation. Old devices will no

Use hardware timer to simulate interrupt moderation.  Old devices will no
longer be livelocked when they are receiving on GigE line.  Newer devices
also gain well controlled interrupt rate.

If hardware supports interrupt moderation (e.g. 8168B, 8168C), you could
also use hardware based interrupt moderation, however, due to lack of
necessary information it does not work as reliably as simulated interrupt
moderation.  It is _not_ recommended currently.

By default, PCI-E devices' simulated interrupt moderation timer is set to
75us, while PCI devices' is set to 125us.